The Kelp Cultivation Potential in Coastal and Offshore Regions of Norway
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ORIGINAL RESEARCH published: 18 January 2019 doi: 10.3389/fmars.2018.00529 The Kelp Cultivation Potential in Coastal and Offshore Regions of Norway Ole Jacob Broch 1*, Morten Omholt Alver 1, Trine Bekkby 2, Hege Gundersen 2, Silje Forbord 1, Aleksander Handå 1, Jorunn Skjermo 1 and Kasper Hancke 2 1 SINTEF Ocean, Trondheim, Norway, 2 Norwegian Institute for Water Research (NIVA), Oslo, Norway We have evaluated the cultivation potential of sugar kelp (Saccharina latissima) as a function of latitude and position (near- and offshore) along the Norwegian coast using a coupled 3D hydrodynamic-biogeochemical-kelp model system (SINMOD) run for four growth seasons (2012–2016). The results are spatially explicit and may be used to compare the suitability of different regions for kelp cultivation, both inshore and offshore.The simulation results were compared with growth data from kelp cultivation experiments and in situ observations on coverage of naturally growing kelp. The model Edited by: demonstrated a higher production potential offshore than in inshore regions, which is António V. Sykes, Centro de Ciências do Mar (CCMAR), mainly due to the limitations in nutrient availability caused by the stratification found along Portugal the coast. However, suitable locations for kelp cultivation were also identified in areas with Reviewed by: high vertical mixing close to the shore. The results indicate a latitudinal effect on the timing Mark Johnson, National University of Ireland Galway, of the optimal period of growth, with the prime growth period being up to 2 months earlier Ireland in the south (58 ◦N) than in the north (71 ◦N). Although the maximum cultivation potential Oscar Sosa-Nishizaki, was similar in the six marine ecoregions in Norway (150–200 tons per hectare per year), Ensenada Center for Scientific Research and Higher Education the deployment time of the cultures seems to matter significantly in the south, but less (CICESE), Mexico so in the north. The results are discussed, focusing on their potential significance for *Correspondence: optimized cultivation and to support decision making toward sustainable management. Ole Jacob Broch [email protected] Keywords: Saccharina latissima, macroalgae cultivation, mathematical model, offshore aquaculture, ecosystem model, marine biomass, environmental variables, latitude Specialty section: This article was submitted to Marine Fisheries, Aquaculture and INTRODUCTION Living Resources, a section of the journal In order to meet the future challenges of limited terrestrial food resources, a greater part of the Frontiers in Marine Science human food consumption will need to be based on marine production, at lower trophic levels than Received: 09 October 2018 today (Olsen, 2011). The demand for marine biomass for other purposes, such as biofuels, feed Accepted: 31 December 2018 for animals, cosmetics, medicines, pharmaceuticals and raw materials for the biotechnological Published: 18 January 2019 industry, is also expected to increase (Holdt and Kraan, 2011; Kraan, 2016). Citation: Macroalgae are, by volume, the largest group of species in aquaculture, with a global Broch OJ, Alver MO, Bekkby T, production of 2.94 × 107 tons wet weight per year (FAO, 2018). More than 99.9% of Gundersen H, Forbord S, Handå A, this is produced in Asia (Ibid.), but the interest in macroalgal aquaculture in the Western Skjermo J and Hancke K (2019) The Kelp Cultivation Potential in Coastal hemisphere is increasing. It has been suggested that by 2050, the value of the kelp industry 9 and Offshore Regions of Norway. may have a turnover of 4 × 10 Euro per year in Norway alone, with a production of 7 Front. Mar. Sci. 5:529. 2 × 10 t per year (Olafsen et al., 2012). Globally, the potential for marine macroalgal doi: 10.3389/fmars.2018.00529 cultivation has been suggested to lie at 109 to 1011 t dry weight (DW) (Lehahn et al., 2016). Frontiers in Marine Science | www.frontiersin.org 1 January 2019 | Volume 5 | Article 529 Broch et al. The Kelp Cultivation Potential in Norway There are many sectors and interests competing for space results from both cultivation experiments with S. latissima and in coastal regions (Hersoug, 2013), including cultivation of surveys of the density of natural kelp populations in order to macroalgae (Duarte et al., 2017). In order to manage the provide an evaluation of the realism of the results. coastal zone, tools that can assess the suitability of different locations for different purposes are necessary. In order to grant MATERIALS AND METHODS aquaculture permits for macroalgae production, knowledge of the production potential and spatially explicit maps of suitable Coupled Hydrodynamic-Ecosystem-Kelp areas for production are needed. These maps must be based on Model System (SINMOD) physical, biological and biogeochemical variables important for Model Description the survival and growth of macroalgae. While most naturally SINMOD is a coupled 3 dimensional hydrodynamic- growing macroalgae depend on some form of solid substrate biogeochemical model system (Slagstad and McClimans, 2005). and therefore grow mostly on the bottom as deep as the The biogeochemical component includes compartments for, e.g., − + light penetration allows, macroalgal cultivation facilities may in concentrations of nitrate (NO3 ), ammonium (NH4 ), silicate, principle be sited regardless of the seabed depth. This allows detritus, bacteria, phytoplankton, ciliates and zooplankton for great possibilities in the choice of cultivation sites and fewer (Wassmann et al., 2006). Phytoplankton production and nutrient direct conflicts with natural macroalgal communities. uptake are calculated as combined effects of temperature, light, Kelps are among the most important macroalgae in and nutrient concentrations. The phytoplankton is grazed aquaculture. The main environmental variables for the growth by ciliates and zooplankton, and dead/respired matter enter of kelps are nutrients, light, temperature, and ocean currents the detritus and ammonium compartments and are further (Wiencke and Bischof, 2012). For naturally growing kelps, wave remineralized into nitrate and silicate. The attenuation of light exposure is also important, since waves keep the fronds free from is calculated from the background attenuation of the sea water sedimentation and epiphytic growth, while maximizing the light and the concentration of phytoplankton. The details are given in trapping area and sustaining a good flux of nutrients. Wassmann et al. (2006). Biogeochemical conditions are determined by physical factors. An individual based growth model for sugar kelp has been The Norwegian Coastal Current (NCC) is one of the main developed and coupled with SINMOD (Broch and Slagstad, 2012; physical drivers of the Norwegian coastal ecosystem. The NCC Broch et al., 2013; Fossberg et al., 2018). The state variables is driven by the outflow from the Baltic Sea and transports water in the growth model are frond area (A, unit: cm2), internal northward along the Norwegian coast where it gets replenished nitrogen reserves (N, unit: g N (g structural mass)−1), and with freshwater and nutrients from rivers and fjords along the internal carbon reserves (C, unit: g C (g structural mass)−1). way (Sætre, 2007). This leads to periods of strong stratification, The environmental variables used to force kelp growth in the especially in fjords and in the NCC itself, and thus to nutrient model are temperature, salinity, light intensity (PAR), nutrient − + depletion in the surface layer in spring/early summer following (NO3 , NO4 ) concentrations, water current speed and latitude the pelagic spring bloom. This has implications for the nutrients (implicitly through the day length) (Broch and Slagstad, 2012; available for macroalgal primary production. Broch et al., 2013; Fossberg et al., 2018) (Figure 1). Salinities The main objective of the present paper was to investigate below 25 PSU are assumed to cause reduced growth, nutrient how the aquaculture production potential for the commercially uptake and photosynthetic rates (Bartsch et al., 2008; Mortensen, important kelp species Saccharina latissima varies along and 2017). This effect has been introduced in the model by outside the Norwegian coast. While there have been many multiplying those rates by the factor surveys on the production and biomass in natural kelp forests in Norway (Abdullah and Fredriksen, 2004; Moy et al., 2009; Gundersen et al., 2012), information on the cultivation potential 1, for S ≥ 25 S−25 for kelps outside natural kelp forests is largely missing on fsalinity = 1 + 18 , for 16 ≤ S < 25 S a coastal scale. In absence of large, high resolution data 32 , for 0 ≤ S < 16 sets on industrial cultivation yields, a coupled hydrodynamic- where S denotes the salinity (PSU). biogeochemical ocean model system (SINMOD; Wassmann The effect of water current speed has been modified from that et al., 2006) was used. The model has been further coupled in Broch et al. (2013). In the present version, the uptake rate of with an individual based growth model for S. latissima (Broch nutrients, J, is calculated as et al., 2013; Fossberg et al., 2018). Although dynamical modeling can never replace field experiments and surveys, the simulations provide results resolved in time and space that are especially J = fcurrentJN useful in “data poor” contexts. Thus, both geographic and seasonal/interannual variations in the cultivation potential are where JN is the uptake rate per unit frond area based on external considered, in addition